Unit 2, L13 Hormonal Regulation of Body Water Flashcards
ADH is synthesized where
In the hypothalamus, in the paraventricular and supraoptic neurons
Where does ADH get released
It gets released from the posterior lobe of the pituitary
How does ADH spread throughout the body?
The posterior lobe of the pituitary is very close to blood vessels, so ADH is secreted directly into the blood stream, so the hormone can spread throughout the body
ADH’s production is dependent on the body sensing in 2 different regions
1) Baraoreceptors
2) Hypothalamus itself
ADH is released in response to what two things
1) Extracellular hyperosmolality
2) Volume depletion
Sensors of ADH
Hypothalamic osmoreceptors are the OVLT and the SFO, they stimulate production and ADH release
Aortic arch and carotid baroreceptors inhibit ADH release
Effector of ADH release
Exocytosis of ADH from terminal axons of supraoptic neurons and paraventricular neurons into blood of the posterior pituitary
Target of ADH release
Extracellular ADH receptors in distal tubules and collecting duct
Response to ADH release
Increased passive water reabsorption into renal medulla by causing insertion of aquaporins into the tubular epithelial cells
Other factors that affect ADH release
1) Ang II, it stimulates ADH release
2) ANP, it will inhibit ADH release
Healthy adults have an osmolarity of ______
275-290 mOsm/kg, but average is 280-285 mOsm/kg H2O
Above the level of 290 mOsm/kg H2O, what happens to levels of ADH
They rise sharply and linearly with plasma osmolality
How to the thirst receptors tell us to drink water
When the osmolality gets too high, usually around 298 mOsm/kg, it triggers the thirst receptors
What do AQP do
Mediate reabsorption of water, found on both basal and apical sides
Mechanism of insertion of AQP in the cell membrane
AVP will bind to the V2 receptors on the blood side, since its being released by the posterior pituitary into the blood supply. This is through the peritubular capillaries, and these will interface with the epithelial cells that make up the tubules. This will cause a signaling cascade of increasing cAMP to produce PKA. PKA will work 2 ways, first to put ready-made AQP into the membrane, and second, can stimulate activation of transcriptional factors that allow for more AQP to be synthesized and put into the membrane. AQP2 is on the lumenal side, on the urine side, which will allow water to go into the cell. There are also other AQP receptors on the basal side of the cell, towards the blood, to let the absorbed water to move back into the blood
Walk through the mechanism of dehydrating someone (ethically)
Depriving someone of H2O will cause an increase in plasma osmolarity. This will stimulate the osmoreceptors in the hypothalamus, causing ADH secretion. This will go into the blood supply, activating the AVP receptors and starts the downstream signaling cascade, resulting in AQP being inserted into the cell membrane. This causes the cells to facilitate water reabsorption in the distal part of the kidney. Urine osmolarity then goes up because you are extracting water but leaving salt behind, so you are concentrating the salt and urine volume goes down. This will decrease the plasma osmolarity towards normal. Additionally, there will be activation of the thirst receptors
What is the pathway that happens when drinking 1 liter of water per hour?
Drink H2O, this will decrease plasma osmolarity. This will cause inhibition of the osmoreceptors in the anterior hypothalamus, so decrease production of ADH. This decreases secretion of ADH from the posterior pituitary, which decreases H2O permeability of the principal cells. This decreases H2O reabsorption from the urine, decreasing urine osmolarity and increasing urine volume. This leads to an overall increase in plasma osmolarity towards normal. There will also be inhibition of the thirst receptors
Central (pituitary) diabetes insipidus
Insufficient AVP release, possibly through damage to the hypothalamus. Manifests as polyuria and polydipsia
Nephrogenic diabetes insipidus
The AVP receptor 2 (V2) is found in the kidney and its being effected through a mutation. Manifests are polyuria and polydipsia
Syndrome of inappropriate ADH secretion (SIADH)
Very high water retention, and there are multiple causes of SIAD. Overproducing ADH, causing more AQP to be inserted, allowing for more water to be reabsorbed
Total body water is approximately _______% of body weight
60%
Total body water is distributed into two compartments
Intracellular fluid - 2/3
Extracellular fluid - 1/3
Major cations and anions in the intracellular fluids
Major cations are K+ and Mg2+
Major anions are protein and organic phosphates
Major cations and anions in the extracellular fluid
Major cation is Na
Major anions are Cl- and HCO3-
If the TBW is 60%, what is the breakdown of ICF and ECF?
ICF is 40% and ECF is 20%
Equation for measurement of fluid volumes by the dilution method
V space = (AmtX given - AmtX lost)/ equilibrium [X] in space
Measure TBW with what
D2O
Measure ECF water with what
Radiosodium or radiosulfate
Measure P water with what
Evans Blue (T-1824)
Calculate IC water with what equation
TBW - EC water
Calculate IS water with what equation
EC water - P water
What is a Darrow-Yannet Diagram
Body fluid osmolarity being plotted against body fluid volume
What are the three steps for solving a fluid balance problem
1) Construct the Darrow-Yannet diagram
2) Draw the disturbance (this only happens to the ECF)
3) Equilibrate the ICF and the ECF by moving water from hypotonic to hypertonic (the water shift may be ECF to ICF or ICF to ECF)
What will happen to the Darrow-Yannet Diagram if there is hyperosmotic volume expansion
It will shift right and taller
What will happen to the Darrow-Yannet Diagram if there is Isomotic volume expansion
Expand to the right side
What will happen to the Darrow-Yannet Diagram if there is hyposmotic volume expansion
Squish down and out on both sides
What will happen to the Darrow-Yannet Diagram if there is hyperosmotic volume contraction
Squish in on both sides and get taller
What will happen to the Darrow-Yannet Diagram if there is isosmotic volume contraction
Squish in on the right side
What will happen to the Darrow-Yannet Diagram if there is hyposmotic volume contraction
Squish down and shift left
What is the equation for the anion gap
[A-] = Na+ - Cl- - HCO3-
What is the breakdown of anions (think anion gap)
Cl-, for 104 mEq/L
HCO3-, for 24 mEq/L
Other anions, 12 mEq/L
What is the anion gap
The difference between measured cations and the measured anions in plasma or urine
